The present invention relates to an electromagnetic actuator device, in particular for the selection of the needles in a knitting machine.
Devices for the selection of the needles in knitting machines are known, which comprise a plurality of needle selection levers positioned superimposed to one another on a plurality of levels, and selectively swinging around respective parallel, horizontal axes between a resting position, in which position an end of the same levers is at an intermediate level between levels of selection butts of needle selection members, and does not interfere with them; and a working position, in which such an end is at the level of a corresponding level of needle butts, and engages the selection butts of said level by pushing the relevant selection members into a non-working track, in which they do not lead the corresponding needles to generate the loop.
The orientation of the selection levers is generally carried out by means of electromagnetic actuators, each of which is associated to a respective selection lever, and is selectively excited according to a pre-established program of needle selection.
The actuators may act on the respective selection levers either directly, or through relevant armatures, the swinging movement of which is transmitted to the levers by means of a geometrical coupling between one end of the armature, and one end of the relevant needle selection rocker lever, e.g., as disclosed in U.K. patent application No. 2.008,157.
These electromagnetic-control selection devices show the advantage that the type of selection can be rapidly modified by simply changing the sequence of the control impulses sent to the various electromagnets by an electronic equipment, which can be programmed from time to time according to the desired sequence.
However, the electromagnetic actuators, which are necessary in a number equal to the number of the selection levers, involve problems of dimensions, because, owing to power reasons, the size of the electromagnets cannot be reduced under certain limits, otherways the action of magnetic attraction will be insufficient for the intended purposes.
The higher and higher speeds of the knitting machines require higher and higher actuation speeds, and, consequently, the moving masses and the frictions to be more and more reduced. The high number of oscillations of the moving members involves continuous impact stresses, and hence a considerable wear of the relevant members, with a loss of precision.
In case a fault occurs to one of the actuators, the operation of replacement of it is mostly complex and difficult, and hence long, with times of inactivity of the selection device, and of the relevant knitting machine, which result in increases in the production costs.